C# Signature:

[DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName,int nMaxCount);

VB.NET Signature:

<DllImport("user32.dll", CharSet:=CharSet.Auto)> _
Private Shared Function GetClassName(ByVal hWnd As System.IntPtr, _
   ByVal lpClassName As System.Text.StringBuilder, _
   ByVal nMaxCount As Integer) As Integer
    ' Leave function empty    
End Function

Alternate VB.NET Signature:

Public Declare Auto Function GetClassName Lib "User32.dll" (ByVal hwnd As IntPtr, _
    <Out()> ByVal lpClassName As System.Text.StringBuilder, _
    ByVal nMaxCount As Integer) As Integer

VB Signature

Public Declare Function GetClassName Lib "user32" Alias "GetClassNameA" _
         (ByVal hWnd As Long, _
          ByVal lpClassName As String, _
          ByVal nMaxCount As Long) As Long

Notes:

In .NET Framework 4.0, only CharSet.Ansi seems to produce the result.

The return type int seems to crash the .NET application in 64-bit mode (occasionally), long seems to work better. Maybe it should even be IntPtr? Please modify this note if you have more insights.

Tips & Tricks:

Please add some!

Sample Code:

C# Sample Code

private static bool isIEServerWindow(IntPtr hWnd)
{
    int nRet;
    // Pre-allocate 256 characters, since this is the maximum class name length.
    StringBuilder ClassName = new StringBuilder(256);
    //Get the window class name
    nRet = GetClassName(hWnd, ClassName, ClassName.Capacity);
    if(nRet != 0)
    {
        return (string.Compare(ClassName.ToString(), "Internet Explorer_Server",true,CultureInfo.InvariantCulture) == 0);
    }
    else
    {
        return false;
    }
}

VB.NET Sample Code

Create a new VB .NET form and add a button Button1 to it.

Private Sub Button1_Click(ByVal sender As System.Object, _
    ByVal e As System.EventArgs) Handles Button1.Click
   Dim sClassName As New StringBuilder("", 256)
   'pass in the handle of the object for which to get
   'the class name; for example, the form's handle
   Call GetClassName(Me.Handle, sClassName, 256)
   MessageBox.Show(sClassName.ToString)
End Sub

Alternative Managed API:

The ManagedWindowsApi project (http://mwinapi.sourceforge.net) provides a

class ManagedWinapi.SystemWindow that has a ClassName property.